Stringed instruments all have an elongated neck over which extend a plurality of spaced-apart longitudinal strings which are tied or otherwise fastened under tension at their opposite ends. The instruments to which this invention is particularly directed include guitars, banjos, mandolins, etc., i.e. those types of stringed instruments having frets on the fingerboard. A fret is a thin transverse bar embedded in the wood of the fingerboard which the musician uses to sound a desired note by pressing with a finger on a string immediately behind a fret. (For descriptive purposes, the soundbox of the instrument will hereinafter be referred to as the "forward" end of the instrument, while the head of the instrument will be called the "rear" end).
The invention is also directed, however, to stringed instruments without frets, such as those of the violin family.
A capo, then, is a device having a pressure member urged towards contact with all the strings, transversely thereto and behind a fret, as is well known. The prior art teaches many such capos, all of which are adapted to shorten the effective length of the strings to raise their pitch and also vary the timbre of the sound as desired. For example, the subject of the U.S. Patent to Myerson et al issued on Feb. 24, 1981 and bearing U.S. Pat. No. 4,252,046 teaches a capo having a pressure bar 16 having differently-shaped surfaces adapted to press against the strings and secured in place by an elastic mounting strap 18. The pressure bar 16 of this Patent would be relatively expensive to manufacture. Moreover, there is a possibility that sliding the capo from one fret to another might result in uneven pressure exerted on the strings by the pressure bar if the latter is even slightly transversely disaligned. The result is that one or more of the strings would be "bent" ("bending" of a string means transverse movement thereof at a given point on the fingerboard, which raises slightly the pitch of the string). Thus, the relative pitches of the strings would change, putting the instrument out of tune.
It will be noted that there is no adjustment means for the tension of mounting strip 18. Another undesirable possibility, therefore, is that moving the capo forwardly or rearwardly will cause one or more of the strings to "buzz" against the selected fret due to the fact that the neck of a stringed instrument tapers gradually rearwardly, thereby changing the tension exerted by the mounting strap 18. At best one or more strings might sound unclearly if not actually "buzz".
The two above-mentioned undesirable possibilities, namely string "bending" and/or "buzzing" are common to all sliding or slidable capos in the prior art because of their basic design. The design predominantly consists of some kind of string-contacting pressure bar biased against the strings by an elastic member passing around the neck of the instrument and secured to prongs projecting transversely of the pressure bar at its opposite ends. For example, reference can be had to the U.S. Patent issued to Cahn Aug. 28, 1979 and bearing U.S. Pat. No. 4,165,670; the U.S. Patent to Hutchins issued Jan. 20, 1976 and bearing U.S. Pat. No. 3,933,073 (the latter Patent being of different design); the U.S. Patent issued to Valentino on Mar. 27, 1973 and bearing U.S. Pat. No. 3,722,346; and the U.S. Patent granted to Utt on May 23, 1897 and having U.S. Pat. No. 583,102.
As for those capos which are not conceived as being easily slidable, being rather temporarily lockingly positioned at a given fret, their main disadvantages are that two hands are required to move the capo when needed and that they must be readjusted at each new fret.
One further disadvantage is that, until now, all capos have been completely removed from the instrument when not needed and, hence, must be kept somewhere if they are not to be lost.